It's the pressure. Not uncommon at all. The thought that his virility is under scrutiny is probably pretty off-putting.
Better if you don't time it and make a big build up in this way. Don't announce to him that tonights the night and he must impregnate you now or never! Just have lots of sex all throughout the month, every other or couple of days. No pressure on him and plenty of orgasms for you! Hopefully you'll get a baby before too long as well.